countercurrent multiplier

Pronunciation: kown'ter-ker'ent mul'ti-pli'er

Definition: A system in which energy is used to transport material across a membrane separating two countercurrent multiplier tubes connected at one end to form a hairpin shape; by this means a concentration can be achieved in the fluid in the hairpin bend, relative to the inflow and outflow fluids, which is much greater than the transport mechanism could produce between the two sides of the membrane at any point; the nephronic loops in the renal medulla act as countercurrent multipliers.